Mike4 wrote:richlist wrote:Just to clarify....There are 3 main types of electric vehicles.
* BEV.....battery electric vehicle. Fully electric.
* PHEV....plug in hybrid electric vehicle. Has engine and electric. Battery charged by plugging into grid.
* HEV.....hybrid electric vehicle. Has engine which charges the storage battery. Does not plug into grid.
Not according to Nocton above. S/he says the engine in a HEV connects via a clutch to the wheels. No mention of the engine charging the battery.
Probably every HEV has its own quirks.
The Prius which Mike4 mentioned was a brilliant piece of engineering. It charged the battery using the engine. In simple terms a planetary gear system distributed power between the wheels, the alternator, the petrol engine and the electric motor depending on where it was needed, with computer control of the power output of the engine and motor based on the charge state of the batteries, the acceleration or braking demand (changing kinetic energy) and the changing potential energy (going up- or downhill). So the Prius could charge the battery while slowing down, converting kinetic energy back to electrical; or while going downhill, converting potential energy to electrical; or by running the engine, converting fossil fuel into electrical energy. A large part of their efficiency came because the petrol engine 1. could be smaller (thus lighter, more efficient), 2. was optimised for a particular role i.e. cruising not accelerating and 3. only charged the battery while running at its maximum efficiency.
Here's a simple scenario to contrast the Prius hybrid with a petrol vehicle: imagine starting from a traffic light, reaching a steady speed for a few minutes, then stopping at the next light.
1. The traditional petrol car's engine would be larger than the hybrid's because it would be required to accelerate the vehicle unaided. It would also be designed with torque as well as power in mind, i.e. with some efficiency compromises. As the car accelerated the efficiency of the engine would vary (i.e. become less than optimal) depending on the engine speed but mitigated by changing gear (but... heavy gearbox). At cruising speed the engine is still running wasting a small amount of fuel. While braking for the next light, all the speed of the car becomes heat in the brakes or engine, which is still running while slowing and stopped.
2. The Prius hybrid sets off and mostly accelerates with its electric motor, which efficiently produces high torque at low speeds. The petrol engine helps but can be smaller and work efficiently because of the contribution of the electric motor. The control computer varies the electric motor output while gaining speed to keep the petrol engine in its efficient sweet spot. While cruising the engine continues running in its sweet spot, recharging the batteries whose energy has been used for acceleration. When the charging is complete the petrol motor is turned off entirely, the small amount of power needed to overcome air resistance can be supplied by the electric motor. If the speed/slope is such that the computer judges the petrol engine would be more efficient than the electric motor, then the former is restarted and the electric motor's contribution reduced. As the car slows for the lights the engine is still turned off while the battery is charged further using the reducing kinetic energy. The engine remains off while waiting at the lights.
Incidentally, the Prius also lacked a starter motor because the electrical drive motor could start the engine. Alternatively you could think of the drive motor as an oversized starter motor connected directly to the drive train via those planetary gears. Thinking about it, the only real additional part for the Prius is its large solid state battery, otherwise the parts list is similar:
-it has a smaller acid battery than the petrol car (not used for starting the engine)
-it has a smaller, more efficient petrol engine
-it has a larger electric motor, used for propulsion as well as starting the engine
-it has a planetary gear system and computer controlled power versus a gearbox (manual or auto)
-its brake pads last longer, but it has the additional battery pack.
That's probably way more than you wanted to know but hopefully gives and idea of the many ways that efficiency was improved by the Prius's design.
GS